Well when I was 19 I dated a girl who was 23, I recently dated a girl who's now 21 (i'm 23), and I'm now kinda-sorta interested in a girl who is about to turn 19. I think a four-year difference is okay. Though it really does depend on their (and my) status in life. When I was 20 I cowered to the thought of a 'commitment'. Now it's a different story.